1. Field of the Invention.
This invention generally relates to air parking brakes for vehicles. More particularly, this invention relates to a device for automatically "locking" an air parking brake in a safe, engaged condition during times when it is not safe for the vehicle to move. This automatic engagement and locking of the air parking brake may be actuated by signals from various circuits and sensors inside and outside the vehicle.
2. Related Art.
Numerous types of vehicles employ what is called an "air parking brake". Simply put, an air parking brake system is comprised of three main parts: an air source, a valve and the brake itself, which is a spring-actuated brake that is disengaged by air pressure acting against the spring(s). When the valve is open, called a loading valve, air is supplied to the brake, thereby releasing the brake and allowing movement of the wheels of the vehicle. When the valve is closed, air pressure is relieved from the brake through an exhaust vent and the spring engages the brake, thereby inhibiting movement of the wheels of the vehicle.
An example of such an air parking brake system exists in commonly used commercial vehicles, such as trucks, commercial buses, or school buses. In such vehicles, an air compressor compresses air, which is stored in a reservoir or tank. This air is then directed to a loading valve through a supply hose and on to the parking brake mechanism through a delivery hose. This loading valve has a handle that extends from the dashboard of the vehicle, allowing the vehicle operator to "Pull To Apply" or "Push To Release" the parking brake.
"Pulling" the loading valve handle closes the loading valve, cutting off the air pressure coming from the reservoir or tank. Air pressure in the delivery hose (between the loading valve and the parking brake) is released automatically through use of an exhaust vent built into the loading valve. When air pressure is absent from the air parking brake, brake springs hold the brake pads against the brake drum, thereby inhibiting the rotation of the vehicle's wheel(s).
"Pushing" the loading valve handle opens the loading valve, allowing air pressure to reach the air parking brake. When air pressure is applied to the air parking brake, the air pressure overcomes the tension of the brake springs holding the brake pads on the brake drum, and the air parking brake is released, allowing rotation of the wheel.
The inventor is aware of several conditions and events in and around a vehicle that create the potential for danger if the vehicle moves during the condition or event. The inventor is also aware that conventional safeguards against unwanted vehicle movement are less than optimum. For example, a conventional, engaged air parking brake may be accidentally released by someone accidentally bumping into the loading valve handle or otherwise inadvertently or intentionally pushing the loading valve handle. If this happens when the vehicle is parked on a hill, the vehicle may roll down the hill, causing the potential for injury/damage to passengers and to people and property in its path.
Another dangerous event occurs when a vehicle operator fails to set the parking brake before leaving the driving seat, with or without the vehicle engine running. By leaving the driving seat, he/she leaves the position from which he/she may quickly regain control of the vehicle if it begins to move at an inappropriate time. Therefore, because it is a manual system and vulnerable to operator error, the conventional air parking brake system is less than optimum, and can again result in injury to people and damage to property.
Other potentially dangerous conditions exist when people are entering or leaving a vehicle. For example, during use of a wheelchair lift, the individual in the wheelchair and any assistants near the lift are in risk of being injured if the vehicle moves suddenly or unexpectedly. Or, school children or adults are at risk when entering or leaving a bus, if the bus moves, either because the bus begins rolling down a hill or because the driver does not realize the individual is in or near the door. School children or adults are also at risk if an emergency door, for example, at the back of a school bus, is opened and the bus moves ahead.
There are instances of parking brake locking systems in the patent literature, but none are as simple, effective, and safe as that envisioned by the present inventor. None of the prior art locking systems include the comprehensive safety features of the present invention. None of the prior art devices feature the fail-safe systems of the present invention, which preferably override other signals, except for a vehicle movement sensor system, to apply the spring-actuated parking brake.
One patent shows an invention for keeping an air parking brake from being accidentally, inadvertently, or intentionally disengaged. U.S. Pat. No. 5,688,027 (Johnson) discloses a "control valve lock for a vehicle air brake system." Essentially, Johnson describes a box that locks over the top of the valve handle impeding the release of the parking break until the box is unlocked. A disadvantage of the Johnson invention is that the operator must take separate steps each time the brake is to be locked, through the use of the box and the additional key.
There are inventions for the automatic engagement of parking brakes upon the turning off of an ignition or engine key switch. U.S. Pat. No. 5,624,352 (Smale) discloses an "ignition-controlled parking brake interlock." This lever and latch interlock invention is activated by turning off the vehicle ignition key. U.S. Pat. No. 5,675,190 (Morita) discloses an "operating apparatus for parking brake and method for releasing parking brake." The Morita invention uses a combination of the vehicle ignition key switch, with ON-OFF positions, and a three-way parking brake switch with ON-OFF-RESET positions, to engage the parking brake. A drawback of the Morita invention is the complexity incumbent in the use of its multiple switches.
Some vehicle anti-theft devices are designed to prevent brake disengagement by unauthorized persons. U.S. Pat. No. 3,579,285 (Verdier) discloses such a system, entitled "hydraulic anti-theft system for vehicles." The Verdier invention comprises an additional key operated switch, other than the ignition switch, which works to maintain fluid in the brake lines and subsequently pressure on the brakes. A disadvantage of Verdier is the use of an additional key.
U.S. Pat. No. 4,519,653, issued to Smith, discloses an anti-theft lock device, which includes a solenoid for attachment to the outer end of a conventional loading valve. When de-energized, the solenoid moves a lock member into the path of the valve actuating member of the conventional loading valve, physically blocking the actuating member so that it cannot be pushed in to disengage the parking brake. If the conventional loading valve has been disengaged prior to de-energizing of the solenoid, then the solenoid and its lock member are ineffectual, in that the lock member merely slideably contacts the side of the valve actuating member in a non-interfering relationship, and, hence, does not engage the brake or have any effect on the brake. Thus, the Smith device may be used as an anti-theft device, after the driver has manually pulled on the brake and turned off the ignition, but it does not have the automatic emergency safety features of the present invention.
Another U.S. Patent, that issued to Howarth (U. S. Pat. No. 3,174,502), discloses a "theft prevention apparatus." This apparatus employs a ignition switch which, when closed, engages a hydraulic brake system.
While inventions exist for the control of brakes in general, none combine ease of use and simplicity of manufacture/installation with both safety and theft deterrence. None include the automatic brake engagement and locking features that prevent dangerous movement during the everyday operation of many vehicles and make everyday operation safer for the vehicle drivers and the public.